It is known in the prior art selectively to plate metals, particularly noble metals, upon conductive workpieces such as metals or semi-conductors, by a process known as brush plating. Typically the workpiece is moved or wiped along a porous covering which is saturated with an appropriate metal-bearing electrolyte, while the electrolyte is maintained positive and the workpiece negative, thereby limiting the plating to the areas wiped by the porous member. This process has been adapted to mass production processes in which the brush and its electrolyte supply means are stationary and the workpieces are continuously moved along, and wiped against, the porous outer surface of the brush assembly.
Such methods and apparatus are shown and described, for example, in U.S. Pat. No. 4,452,684 of Karl Palnik, filed Mar. 11, 1983 and issued Jun. 5, 1984. In the latter type of system, the main body of the brush is typically made of a porous plastic material, which provides adequate support at temperatures below about 50.degree. C. but which, above that temperature, tends to distort rather easily and thus present to the article to be plated a brush surface which is not straight, resulting in misplaced or otherwise non-uniform plating of the workpieces. However, it has been found that plating efficiency and speed are enhanced if the electrolyte can be maintained at temperatures in a higher range of about 50.degree. to 83.degree. C. Accordingly, the above-mentioned tendency toward dimensional instability of the main body of the brush of the prior art at temperatures above about 50.degree. C. has prevented commercial operation in this advantageously higher temperature range.
Further, it has been found that it is often desirable to present different configurations of brush to the workpiece, depending upon the nature of the workpiece and upon what kind of plating is to be accomplished. For example, at times a nearly V-shaped edge on the brush may be appropriate, and at other times an edge having a rounded or flat surface, or even having a recess therein, may prove desirable. In the arrangements of the prior art, such changes in shape required complete replacement of the main body of the brush with another main body, which is extremely inconvenient, and requires an inventory of different main brush bodies suitable for different workpieces.
Further, in prior-art apparatus for brush plating, an electrolyte pressure was applied to opposite ends of a perforated electrolyte conduit extending through the brush body, to force the electrolyte outwardly from the conduit through the porous brush body to the surface, where it suffused a felt-like porous cover which in turn contacted the workpiece. The permissible rate of inlet flow of electrolyte was in this case limited, for example to about 4 liters per minute, because the brush and cover could not absorb electrolyte at a higher rate. With such relatively low flow rates, it was found that the temperature of the electrolyte dropped significantly, and somewhat uncontrollably, as it passed slowly through the conduit and outwardly through the main body of the brush. This made it difficult to achieve higher, accurately-controlled electrolyte temperatures.
In addition, the previously known brush described in the above-identified patent was not readily adjustable to plating of objects at different angular positions about the longitudinal axis of the brush e.g. above the brush as compared to beside the brush, nor was it readily and accurately adjustable with respect the distance of the brush from the path of the workpieces. Such capability is desirable to obtain the best operating conditions for any particular application.
Furthermore, in the prior art there has been room for improvement with respect to the application of the anodic voltage to the electrolyte in the brush cover, particularly with regard to efficiently and uniformly charging the electrolyte adjacent the workpiece. It has also been difficult to provide effective cathodic connection to the workpiece as it moves along the brush, and to assure positive contact between the workpiece and the brush, as desired.
Accordingly, an object of the present invention is to provide new and useful method and apparatus for the brush plating of workpieces.
Another object is to provide such method and apparatus which are operable at higher electrolyte temperatures than were previously usable in similar apparatus, thereby permitting faster electroplating.
Another object is to provide such method and apparatus in which the contacting portion of the brush can be changed easily, rapidly and inexpensively to apply different shapes of brush to the workpiece, for different purposes.
A further object is to provide such method and apparatus in which the desired high temperatures of electrolyte can be provided and accurately controlled.
Still another object is to provide an arrangement which is particularly efficient and effective as the anode in the electroplating process.
Another object is to provide an improved method and apparatus for contacting the workpiece to supply it with cathodic potential, and to assure good contact between workpiece and brush cover.